Initial commit: hardened DeerFlow factory

Vendored deer-flow upstream (bytedance/deer-flow) plus prompt-injection
hardening:

- New deerflow.security package: content_delimiter, html_cleaner,
  sanitizer (8 layers — invisible chars, control chars, symbols, NFC,
  PUA, tag chars, horizontal whitespace collapse with newline/tab
  preservation, length cap)
- New deerflow.community.searx package: web_search, web_fetch,
  image_search backed by a private SearX instance, every external
  string sanitized and wrapped in <<<EXTERNAL_UNTRUSTED_CONTENT>>>
  delimiters
- All native community web providers (ddg_search, tavily, exa,
  firecrawl, jina_ai, infoquest, image_search) replaced with hard-fail
  stubs that raise NativeWebToolDisabledError at import time, so a
  misconfigured tool.use path fails loud rather than silently falling
  back to unsanitized output
- Native client back-doors (jina_client.py, infoquest_client.py)
  stubbed too
- Native-tool tests quarantined under tests/_disabled_native/
  (collect_ignore_glob via local conftest.py)
- Sanitizer Layer 7 fix: only collapse horizontal whitespace, preserve
  newlines and tabs so list/table structure survives
- Hardened runtime config.yaml references only the searx-backed tools
- Factory overlay (backend/) kept in sync with deer-flow tree as a
  reference / source

See HARDENING.md for the full audit trail and verification steps.

deer-flow/backend/docs/SETUP.md

@@ -0,0 +1,92 @@
+# Setup Guide
+
+Quick setup instructions for DeerFlow.
+
+## Configuration Setup
+
+DeerFlow uses a YAML configuration file that should be placed in the **project root directory**.
+
+### Steps
+
+1. **Navigate to project root**:
+   ```bash
+   cd /path/to/deer-flow
+   ```
+
+2. **Copy example configuration**:
+   ```bash
+   cp config.example.yaml config.yaml
+   ```
+
+3. **Edit configuration**:
+   ```bash
+   # Option A: Set environment variables (recommended)
+   export OPENAI_API_KEY="your-key-here"
+
+   # Option B: Edit config.yaml directly
+   vim config.yaml  # or your preferred editor
+   ```
+
+4. **Verify configuration**:
+   ```bash
+   cd backend
+   python -c "from deerflow.config import get_app_config; print('✓ Config loaded:', get_app_config().models[0].name)"
+   ```
+
+## Important Notes
+
+- **Location**: `config.yaml` should be in `deer-flow/` (project root), not `deer-flow/backend/`
+- **Git**: `config.yaml` is automatically ignored by git (contains secrets)
+- **Priority**: If both `backend/config.yaml` and `../config.yaml` exist, backend version takes precedence
+
+## Configuration File Locations
+
+The backend searches for `config.yaml` in this order:
+
+1. `DEER_FLOW_CONFIG_PATH` environment variable (if set)
+2. `backend/config.yaml` (current directory when running from backend/)
+3. `deer-flow/config.yaml` (parent directory - **recommended location**)
+
+**Recommended**: Place `config.yaml` in project root (`deer-flow/config.yaml`).
+
+## Sandbox Setup (Optional but Recommended)
+
+If you plan to use Docker/Container-based sandbox (configured in `config.yaml` under `sandbox.use: deerflow.community.aio_sandbox:AioSandboxProvider`), it's highly recommended to pre-pull the container image:
+
+```bash
+# From project root
+make setup-sandbox
+```
+
+**Why pre-pull?**
+- The sandbox image (~500MB+) is pulled on first use, causing a long wait
+- Pre-pulling provides clear progress indication
+- Avoids confusion when first using the agent
+
+If you skip this step, the image will be automatically pulled on first agent execution, which may take several minutes depending on your network speed.
+
+## Troubleshooting
+
+### Config file not found
+
+```bash
+# Check where the backend is looking
+cd deer-flow/backend
+python -c "from deerflow.config.app_config import AppConfig; print(AppConfig.resolve_config_path())"
+```
+
+If it can't find the config:
+1. Ensure you've copied `config.example.yaml` to `config.yaml`
+2. Verify you're in the correct directory
+3. Check the file exists: `ls -la ../config.yaml`
+
+### Permission denied
+
+```bash
+chmod 600 ../config.yaml  # Protect sensitive configuration
+```
+
+## See Also
+
+- [Configuration Guide](CONFIGURATION.md) - Detailed configuration options
+- [Architecture Overview](../CLAUDE.md) - System architecture